Alien species of animals, fish and plants brought in from abroad are costing the British economy almost £2billion a year, environmental groups have warned.

The invaders are creating a flood risk for riverbanks, killing off our native wildlife and are a constant menace – damaging homes, roads and woodland.

Savage: Killer shrimp, not dissimilar to this one, are causing havoc to the nation's rivers

The Environment Agency has published a hit list of the top ten ‘most wanted’ species which are threatening Britain’s waterways.

The newest and most dangerous of all is the killer shrimp, a two-inch terror with a voracious appetite for fresh water fish.

Native to Eastern Europe, it arrived in England a year ago, probably on dirty fishing tackle.

Chaos: Pennywort is on the environment agency's wanted list - and this is the damage it can do

Other species on the list include water primrose, a pond and aquarium plant; floating pennywort, which grows in shallow lakes and ditches; American signal crayfish, which is endangering our own white-clawed crayfish; and topmouth gudgeon, a tiny fish from Japan.

The list is completed by giant hogweed, Japanese knotweed, Himalayan balsam, mink and parrot’s feather.

The Environment Agency spends more than £2million annually controlling invasive species and that cost is only set to rise.

Altogether, the invaders are estimated to cost the UK economy £1.7billion a year.